Jumpei Yasuda, a journalist who returned to Japan last week after more than three years of captivity in Syria, on Monday gave further details of his time as a hostage, including how he believes another foreigner was also being held at the facility.

The 44-year-old Japanese freelance journalist said that the detention facility was "huge," rising five stories above the ground, and had a basement floor. He thought the building was formerly used as a prison or government office. He also said he heard from a member of a militant group who was serving as a prison guard that the location of the building was Jabal al-Zawiya.

Yasuda has been staying at a hospital since returning to Japan on Thursday night. He is expected to hold a news conference soon, with the media eager to know the details of how he was captured, treated and released by a militant group after going missing following his entry into Syria in 2015.